There has been used an electric power source apparatus including an electric power converter circuit such as an inverter or cycloconverter for converting an output of an electric power source into a predetermined DC output or AC output. For instance, an inverter generator apparatus which is adapted to supply an output of a generator to an inverter and to obtain from the inverter a DC output having a predetermined magnitude or an AC output having a predetermined frequency and magnitude has been used as the generator apparatus having an electric source of a generator driven by a prime mover such as an internal combustion engine.
The inverter circuit used in such an inverter generator apparatus comprises a rectifier to rectify an output of an AC generator, a switch circuit in the form of a bridge circuit of on-off controllable switch elements and a filter circuit to remove an excessive frequency component from an output of the switch circuit. The output of the inverter is applied across the load connection terminals. Such a generator apparatus also comprises a load voltage detection circuit to detect a load voltage across the load connection terminals, a load current detection circuit to detect a load current flowing through the load connection terminals and a controller to control the switch elements in accordance with the voltage detected by the load voltage detection circuit and the load current detected by the load current detection circuit. The rectified output of the generator is adapted to be converted into the DC output having an arbitrary magnitude (an average value) or the DC output of the generator is adapted to be converted into the AC output having arbitrary frequency and magnitude.
In the generator apparatus, the AC output of the generator is converted by the rectifier into a constant DC voltage which is input to the switch circuit. The controller controls the output of the switch circuit by a pulse width modulation (PWM) system by turning on or off the switch elements on upper and lower sides of the bridge circuit while applying a drive signal to the diagonally disposed switch elements of the switch bridge circuit as the switch circuit so as to simultaneously turn on them during a half cycle of a predetermined sine. The voltage output from the switch circuit is applied through the load connection terminals to the load after it is converted into a smooth sinewave voltage through the filter circuit.
The sinewave voltage applied to the load terminals is detected by the load voltage detection circuit and fedback to the controller. The controller compares the instant magnitude of the output voltage with the instant value (the set value) of the predetermined sinewave voltage. The controller generates the predetermined sinewave voltage applied across the load connection terminals so that as the controller judges that the instant value of the output voltage is lower than the instant value of the predetermined sinewave voltage, it increases the duty ratio of the pulse width modulation control and as it judges that the instant value of the output voltage is higher than the instant value of the predetermined sinewave voltage, it decreases the duty ratio of the pulse width modulation control.
Also, the controller controls the overcurrent so that as the load current detected by the load current detection circuit exceeds the set value of the load current or detects the overcurrent, it stops outputting the drive signal applied to the switch elements of the switch circuit. This overcurrent control stops the output of the inverter circuit when the overcurrent flows so as to protect the switch elements of the inverter circuit.
Such an electric power apparatus can provide the voltage of predetermined frequency to the load terminals in spite of the revolution number of the generator because the DC voltage output from the rectifier can be converted into the AC voltage of arbitrary frequency by controlling the inverter circuit. Also, the apparatus can provide the DC voltage of arbitrary magnitude or average value by applying the drive signal to the diagonally disposed switch elements of the switch circuit to control one of the diagonally disposed switch elements to be turned on or off with the predetermined duty ratio.
In case that the volume of the load is relatively large, there are sometimes required to operate the two electric power source units in parallel. In this parallel operation of the two electric power source units, the corresponding two load connection terminals of the two electric power source units are connected to each other so as to simultaneously supply the electric power from the two electric power source units. The voltages generated by the two electric power source units, respectively are required to have the same frequency, the same magnitude and the same phases. If the frequencies or phases of the voltages generated by the two electric power source units are inconsistent due to some causes, the load current introduced from one of the electric power source units flows as the overcurrent into the other electric power source unit. This overcurrent control causes the output of the electric power source circuit to stop, which prevents the load from being normally driven.
It will be conceived that in order to operate the two electric power source units in parallel, the electric power converter circuits of the two electric power source units are controlled by a common controller to prevent the frequencies and the phases from being inconsistent. This will disadvantageously causes the construction of the electric power source units to be more complicated.